And that, ladies and gentlemen, is a demonstration of what we science nerds like to call 'simple science for senators". The amazing thing about it is that you can actually get billions of dollars in funding using this simplified approach when brilliantly researched and written scientific papers fail miserably. Go figure!?!?

Brilliantly written papers are ones that explain the subject matter in an understandable way to the target audience.

You don't send the same paper to theoretical physicist as you send to a senator.

If you don't realize that, you're not anywhere near as smart and clever as you think you are. Do you expect a guy who's job is politics to REALLY ALSO know all the same shit as the guy who spends his entire life working on the physics of it? Are you really that unaware of the people in the world around you not al

Not exactly. Oxygen is a prerequisite for the process known as combustion, since combustion is an oxidization reaction. "A rapid, exothermic oxidation of a substance, called the fuel," is a reasonable definition of combustion. Usually we say the fuel is combustible.

The nitrogen under pressure remains inert, but the oxygen will combust at those levels. There's a great video of the plastic block they were testing with years ago with a huge wall of flame behind it as it traveled at mach 5 iirc...

Actually, do we know that there's any burning going on at all? I believe the light from a fire is not directly emitted by the chemical reaction, it's a result of the combustion gasses glowing from the heat. In which case just heating even an inert gas sufficiently will cause it to glow similarly. And the immense high-speed compression from a mach-7 projectile traveling down a confined tube should generate plenty of heat.

"Flame" is nothing but superheated gases. You can have a flame without combustion if you raise the temperature some other way. In this case it's electrical heating, ram air pressure, and simple air friction.

OK, hot, yes, but wouldn't they need something combustible to actually erupt into flame? Or what am I missing?

I think this is what's going on: when something is burning, the flame you see is just glowing hot air, heated by the energy from the combustion. The flame is not part of the combustion, just the side effect. In this video you see glowing hot air heated by compression and possibly the shock wave from the projectile. Same result, but the energy source is different.

If you've seen a meteor (streak of light in the sky at night, or a visible fireball with a trail if you're really, really lucky), the principle is the same, nothing is burning. The heat come from compression of the air in front of it, and the light you see is from the superheated air in its wake (and a little from the glowing meteorite).

Regarding the background: that is an incredibly high-speed camera, being rotated at a very high speed (think "on a spring"). AFAIK the slug needs to be ferromagnetic. Is uranium? I don't actually know. The sabot is just there to help not destroy the rails and make sure the projectile stays on them (eg doesn't flop out) - it's not meant to help carry the projectile.

The affects on the target when you have something moving that fast are rather dramatic - even plain old steel.

Just speculation but, when you propel something to mach 7, friction becomes a real issue. The SR-71 had a titanium body if I recall correctly, to help deal with temperatures it encountered at Mach 3. It is quite possible that the projectile is very hot and is igniting materials that have lower ignition temperatures.

I suspect it's compression rather than friction doing most of the heating. Much like an orbital reentry vehicle - the gas within the shockwave starts to glow long before it contacts the vehicle itself.

The range means you can fire it from beyond the horizon, so radar can never spot the firing. The speed means you have no way in hell of dodging it or shooting it down. And the kinetic energy of it means no armor will block it, short of armoring the ship to the point it can't move.
Just take aim at the power plant or armory of the other ship and you get a guaranteed kill. I think the key advantage is the inability to be dodged or shot down like a shell, but the range of a missile. Also, I imagine detecting a missile launch is easier then detecting a railgun firing.

traditional aircraft carriers and these will get a lot smaller as drones take place of manned strike craft,

I also believe aircraft carriers will get smaller but not for the reasons you state. I believe that they will get smaller because there will be a greater reliance on vertical lift aircraft, helicopters and tilt-wings. I also believe that aircraft will get faster and have longer range, allowing for lesser reliance on carriers. The politics of flying through nations that might not like to get involved would be solved with aircraft that fly high enough to be considered orbital, and therefore technically in outer space, and therefore flying above "airspace".

Much of that is more about the "how" of shrinking aircraft carriers, the "why" is more about economics. Current carriers are big, slow, and very expensive which makes them easy and tempting targets. For the price of one US Navy aircraft carrier the Navy could have four amphibious assault ships, either choice capable of carrying 80+ aircraft. The amphibious assault ships get cheaper by the dozen but the aircraft carriers cannot, there are only a dozen afloat at any given time which makes economies of scale difficult.

Part of what makes aircraft carriers so expensive is the power plant, nuclear power is expensive. It looks like newer, smaller, safer, reactors which will allow for putting nuclear power in smaller ships, removing the range advantage of the larger aircraft carrier. Addition of jet fuel production systems on board means that they will not need to have oilers come by as often for supplies.

Smaller, faster, cheaper, and still capable of long term missions would be a great alternative to the super carriers we have now. Easier to defend against cannon fire and missiles, due to smaller size. If one is lost or damaged in battle then the reduction in fighting capability is reduced.

I believe your description of sea battles are accurate. The cannon fire is not fast or accurate enough to compete with missiles. Rail guns increase the rate of fire, reduce the weight of the ammunition, and reduce the cost, making it a very good alternative to current missiles and cannons. The range and accuracy of the rail guns might not yet compare to that of the missiles but are still a leap in improvement over cannons.

It means you don't have carry propellant for the shells - propellant that's volatile and dangerous to handle and store. (Historically, the vast majority of Naval ordinance casualties are related to the propellant, not the payload.) You reduce the size, weight, and complexity of the handling path as the size and weight of the round decreases. You also reduce the size of the magazines. (Yes, some of the saved space and weight will be spent on

There are several advantages to railguns for the Navy, in lethality, cost-per-round, how much ammo you can carry, and overall safety.

Lethality - the kinetic energy of a 'passive' round at these velocities is equivalent to or greater than an explosive round (though I would think it might not be all that useful in all circumstances - just flying through some softer materials instead of blowing them up). As the videos show, the 'kill' factor is substantial. The projectiles are also much less affected by gravitational drop and windage - I would think proportional to the velocity - so accuracy will be better. The higher velocity also allows for firing at much longer range - up to 200 miles vs. 30 for the latest 155mm round.

Cost-per-round - while not as cheap as lasers (the laser about to go through sea trials has a cost of about $1 per shot), these systems should have a cost-per-round an order of magnitude cheaper than the big artillery presently in use. (I just read that 155mm shells cost $50,000 each.) It's much easier, cheaper, and safer to build a solid chunk of tungsten or whatever than a huge shell, especially when the savings in transport and necessary safety systems and procedures is taken into account.

How much - the propellant takes up a lot of space, must be stored in special containment that takes up more space. All of that space can be used to store actual projectiles instead, possibly multiplying the number of rounds available by a factor of 5 to 10. Add to that the the higher kinetic energy allows a smaller projectile to be equally effective, which means you can increase the number even more.

Safety - this eliminates the problem of ammunition exploding either in the ship that will use it, or the supply ship. There are many instances of a single 'lucky' hit on a ship that happens to penetrate the ammunition magazines, whereupon that explosion rips the ship in half. The explosives used in ammunition are also toxic. Removing the propellant greatly increases the survival probability in the event of a hit, and eliminates the probability of an unfortunate accident sinking the ship. This also means the supply ships are safer and can deliver much more ammunition in one trip.

Not much room needed for the projectiles, less danger of a powder room exploding, fine. But none of this seems to even mention: what is generating the massive amount of electrical energy required per shot? Not to mention rate of fire - how much time is needed to generate that power for each shot? That this is a very quiet elephant in the room implies it's pretty bad on both counts.

The flight time at mach 7 for 200 miles is about 2.3 minutes, practice your highschool physics and work out how much it drops not allowing for drag.(hint: a LOT). That is assuming no loss of speed (which of course would be SIGNIFICANT).

Which kind of helps, otherwise it could not reach the ground for much of a distance, but hell.. it still needs to be allowed for.

But even worse, the effect of a crosswind along the trajectory path sums over that time also, and that matters as it is much less predictable.This is a kinetic kill vehicle - it needs to hit the target, without terminal guidance. At 200 miles, it simply will not (unless the target it BIG, as in a smalltown..). They will of course try and convince us this is a surgical weapon, however it is not - unless they start using terminal guidance, and good luck gettingelectronics to survive the electromagnetic environment of launch in this thing.

This will of course allow them to more cheaply scattergun an enemy from a nice safe range - go USA!

It's an inert piece of metal that can't be jammed and is probably hard to spot on radar too.

IAAP, although not an expert in rail guns or radar.

I would guess that the projectiles would be hard to detect on radar because they're small. However, it would seem to me that the rail gun itself would send out one hell of a large EMP [wikipedia.org] that would reveal the location of the gun and the time of firing.

The article explains what the major advantages are. Short version, is:

1. The projectiles are inert blocks of metal by necessity of their design, and yet they strike with enough force to cause incredible destruction on impact. (kinetic energy released as mechanical failure of structure, turning into an explosion) which leads to,

2. Inert projectiles are safer to transport for the military. (no one has to sleep on a ship full of explosives)

3. They projectiles are far cheeper to manufacture. (its a block of metal and a sabot, vs the complex things that go into a detonatable round that can be fired a long distance)

4. The range. 100 mile range on these things means they can engage targets without risking the ship itself as much, which is always a plus in combat.

5. One guy can operate it. If you ever watch any footage of large naval guns being fired, it tends to be a multi-person operation to load, fire, and work the gun. Less manpower devoted to a single operation is always helpful.

Assuming you have a big enough capacitor, the output from just one diesel engine should be enough to power a round every 6.5 seconds. There are conversion and efficiency losses, so probably every 15-20 seconds is more realistic.

Also note that 59.6 MJ is about equivalent to 14 kilos of TNT. So the energy yield of this will be on the order of a high explosive round from a 5 inch shell (which weighs about 30 kg), assuming the projectile doesn't pass entirely through the target.

Energy is not the issue – it is the rate of fire. Diesel engines power the supper capacitors, they discharge to fire the gun, and then fill them up again. I have read that this cycle might be measured in minutes instead of seconds. How big of an issue that it will be is a big question.

That depends on how many capacitor banks you've got, yes? Or possibly the sustained power output of the generators, though that's perhaps more of an issue for sustained firing. (Naval ships are pretty big; you can fit a lot of capacitors and generators in there.)

What I'm impressed at is that they can fire the railgun multiple times instead of needing to strip it down and rebuild it each time. That was always the problem with the early railguns; they'd be fine firing once but after that would be so burned up from the currents that they'd be unable to take a second shot on any reasonable timescale. They were cool, but not practical weapons. I'm guessing that that must've been solved, and the result is that pure kinetic weaponry starts to make sense again for ship-level encounters.

Hydrodynamically, they are completely different. A catamaran's hulls displace water at the surface (and below). Its drag consists of both friction and waves generated by that displacement. A SWATH gets buoyancy from completely submerged hulls and minimal distortion of the surface. In the ideal case (hulls are sufficiently submerged), its drag consists entirely of friction.

Normally a SWATH design is used on slow-moving ships where stability is paramount (having the buoyancy underwater means your ship

Smaller diameter projectiles have more drag per unit mass and slow down faster due to air resistance. It's called their ballistic coefficient.

The practice for howitzer-like weapons like railguns is to fire their projectiles in a high arc to get them out of thick atmosphere as fast as possible to reduce air friction. They still won't hit their target at anything like their muzzle velocity even after they recover some kinetic energy on the way back down to target from the top of their parabolic arc.

The ballistically efficient shells from the late-model 15" US Naval rifles had a muzzle velocity of about 3500 feet/second and a flight time to target at maximum range (25 miles or so) of a couple of minutes. Their velocity at impact was half that of their muzzle velocity. I don't see these railgun projectiles achieving anything like that performance as drag increases roughly as the square of velocity and their ballistic coefficient will be a lot less.

Not to nitpick (well.....yah, I'm nitpicking), but both General Atomics and BAE Systems Railguns will be tested on the USNS Millinocket. BAE Systems actually got the Phase II contract, whereas General Atomics did not.

I found it interesting to describe by calculating kinetic energy. A stabbing ~ 185 joules. A gunshot of 45 caliber ACP round ~ 702 joules. A 1 ton vehicle going 100mph ~ 1 megajoule. A giant truck about to hit a series of tubes ~ 30 Megajoules. The kinetic energy of this railgun as it leaves the muzzle ~ 30.9 Megajoules.

1/2mV.terminall^2 since 83 miles away we presume it will be on the downslope of a parabolic-ish arc. 23lb at 300mph - 10kg at 136m/s = 10 x 136^2 = 185kJ give or take. So about the same as a Toyota Yaris going 40mph or a Ford Focus going 35mph.

I presume the 100 mile targets will have to be soft. People are quite soft, as are unarmored vehicles.

Perhaps one of the big benefits of a naval railgun is that it's so difficult to defend against. Old-fashioned anti-ship missiles can be disabled or destroyed by the defending ship's close-in defenses [wikipedia.org]. This is because the incoming missile is filled with sensitive electronics, guidance systems, explosives, fuel, turbojet engines, stabilizing fins, etc, and is very likely to be damaged or destroyed if hit by a 20mm round from the defending ship's CIWS missile defenses.

However, how do you shoot down a hunk of metal traveling at mach 7 toward your ship? It wouldn't make any difference if you hit it with a 20mm round from the goalkeeper [wikipedia.org] or phalanx [wikipedia.org]. The projectile would just keep flying toward the ship and strike it anyways. Besides, how would you even hit something which is so small and traveling at mach 7.

The system's reaction time to a Mach 2 sea-skimming missile such as the Russian SS-N-22 Sunburn from automatic detection to kill is reported to be 5.5 seconds with the firing synchronized to start the engagement at a range of 1,500 m and ending with a kill at 300 m.[2]

The SS-N-22 (russian version) has a 2.6 ft diameter, while the railgun `pellet` appear to be a few inches only, thus being much harder to hit. Also, final speed of the railgun pellet should still be much higher than mach 2. And at t

Imagine if you didn't need to handle explosives like Cordite as propellents anymore. This will reduce storage space and make a battleship's gun turret a while lot safer place to work. One small spark won't set off a magazine anymore.

"Muzzle velocity" is higher, so the distance you can throw something is a bit further, like 5x further. If you can fire further, you have a huge advantage because you can hit your opponent before he can shoot at you. Or if you are doing ground support, you can fire further inland.

I'm assuming a rail gun will be faster to reload. Might take some time to recharge the power supply, but surely we can fire faster than a Mark 7's 2 rounds a minute. More pounds and rounds on the target than your opponent is always better.

Finally, it may be possible to more strictly control forces on the shell when firing it, which may make it possible to put more technology IN the shells, and still get very high velocity. Imagine a shell that can adjust it's flight path, even slightly, which means you can fire in the general direction you want, then fine tune the aim in flight. (I assume they don't do that now..)

Issues to watch out for: First, Rail guns tend to have tracks (rails) and said rails usually have difficulty with wear due to the huge forces and high speeds involved. Hopefully they have engineered the better materials. Second, power supplies for rail guns have to be designed to provide HUGE impulse powers with power generation systems wanting to be running at steady state. You have to match the two. Finally, weapons like this usually mean you have to redesign the whole weapons system, a process that literally takes decades.

Since the navy already runs nuclear reactors on ships I don't think they are that worried about them. However, the capacitor bank exploding could be interesting. I guess they would have to put it somewhere armored on the ship. I would also think that they might have trouble providing cooling for all the electrical equipment as well.

I doubt the capacitors are actually much of a risk either - after all there's no need to have them charged until right before you fire. It'll only be that brief window when they've got a large charge but haven't yet fired that they'll be dangerous. Unlike missiles, conventional explosives, propellants, and fuel which are all a continuous danger as long as they're on board.

The max range of a 155 round is a lot shorter than some are indicating.16000 yards or about 9 miles for the howitzer. It is necessary tonot confuse naval guns with army howitzers. Since I am an Army guyI will not worry about naval guns beyond acknowledging that "guns" havelonger range but the max is about 23 miles.

If somebody asks whether accelerating a 23-lb mass to Mach 7 would push the thing accelerating it backward, we may have to go back to F=ma. And defining m=big and a=very fast seems appropriate. So, yeah, F=big very fast. Not perfect grammar, but at least it paints a picture for our friend who has yet to hear of Newton.

Yeah - Go pedantics! Big can be size, weight, importance, etc... Knee-jerking "big"=="size" is like saying that the "shortest" route home means plowing through walls, cars, etc, rather than going to my car and taking the "quickest" route home. Yes, "fast" is "speed", but when you're referencing F=ma, I think that "getting something big to move fast" implies changing the velocity of a given mass. How close to Kindergarten do we need to get?

There is a youtube video where the weapon is initiated (fired isn't quite appropriate as there is no fire involved) and you can definitely see the barrel recoil within the gun base. The M114, 155mm howitzer firing the M107 he projectile masses at 43Kg and has a muzzle velocity of 564 m/s resulting in at least 24252 Kg*m/s of recoil; the railgun fires a 10 Kg projectile with a muzzle velocity of 2235 m/s resulting in 22350 Kg*m/s or 8% less recoil (power) than a howitzer; 1.3678128e7 J vs. 4.995225e9, but 3

I likely takes a lot more electricity than that because the rail gun isn't going to be very energy efficient. I think I saw a large bank of capacitors in the background of the indoor photo. You wouldn't need such large capacitors, or so many of them, if it was only using 7.2kWh. Also the railgun is also firing a sabot of some sort that contains the 23 pound projectile. Regardless the article already pointed out that it is far cheaper to shoot than the chemically propelled shells. What I really want to see t

Tolerances causes more cost than you think, and documentation around military contract is generally at least half the cost of anything. It's not the contractors taking the piss (what, are you in OZ or UK?), but the government being stupid in supporting the military industrial complex.

Why the hell does an inert slug encased in a discarding sabot cost twenty grand?

The only way these get cheap is if we have to make a lot of them to fight a war. Be thankful we only have to deal with low-rate peacetime economics where the development costs of unique tooling gets amortized across a small number of prototype rail gun slugs creating a big per-unit price tag that causes fools to go apoplectic.

I think the big problem with something like that would be two fold. It would have to be mammoth in size, not just huge. That is becausethe impactor would have to receive all of it's velocity before release, instead of like an ICBM that throttles up once it is in the much thinner upper atmosphere. Missiles don't throttle up until they are at significant altitude because the forces of friction would destroy them at lower altitudes. A rail gun munition would have to be big enough that it could have an effectiv

Depends. How far can your target move in that time. Likely, less than a mile, and since ships don't turn on a dime, they're highly likely to be proceeding on a vector over the coarse of the projectile's flight. So, just like duck hunting, you aim in front of them appropriately, only with computers doing the math for you.